Arresting the phenomenon of heater flooding in a wickless heat pipe in microgravity
Arresting the phenomenon of heater flooding in a wickless heat pipe in microgravity
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DOI：
10.1016/j.ijmultiphaseflow.2016.02.001
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发表时间：
2016-06-01
影响因子：
3.8
通讯作者：
Sicker, Ronald J.
中科院分区：
文献类型：
--
作者：
Kundan, Akshay;Nguyen, Thao T. T.;Sicker, Ronald J.
约束蒸汽泡（CVB）是在国际空间站（ISS）的美国实验室进行的一项透明、无芯热管实验。实验采用40 mm CVB，横截面为3 mm × 3 mm，戊烷为工质，输入功率为3w。由于微重力和建筑材料中的低键数（Bo）， CVB系统非常适合于确定马兰戈尼力对热管极限性能的贡献，透明石英精确地显示了这种限制是如何发生的。先前的文献模型和实验温度和压力测量表明，在足够高的温度梯度下，工作流体应该受到足够的马兰戈尼力，迫使其远离加热器，最终使热端干燥。CVB实验表明，高温梯度导致完全相反的行为，即加热端“泛滥”。加热端溢流是由于加热端高温梯度引起的马兰戈尼诱导流与冷却器回流的毛细管流之间的竞争造成的。这就在试管的加热端形成了一层厚厚的液体层。在流量平衡点，在石英试管的平坦表面上观察到一层厚厚的液体。这被定义为中心落点。从加热器顶部到中心滴的区域称为界面流动区域。当输入功率为0.7W左右时，界面流区逐渐形成，当输入功率为2 W时，界面流区长度逐渐增大。在西点，马兰戈尼部队的兵力饱和。因此，在被淹没的界面区域的力不能推动液体进一步进入毛细区域，液体进一步渗透沿着热管的轴被阻止。当输入功率增加到近3W时，在加热器端附近的蒸汽空间增加到3W。这种行为表明，洪水可能只是达到干涸限制的中间阶段。由于界面力的作用，热端平坦的石英表面被一层波浪形的薄液膜覆盖。最靠近加热器的热端区域是导致冷凝的过热蒸汽区域。附录中讨论了这一附加观察结果。(C) 2016 Elsevier Ltd.版权所有。
The Constrained Vapor Bubble (CVB) is a transparent, wickless heat pipe experiment carried out in the US Labs of the International Space Station (ISS). Experiments were carried out using the 40 mm CVB, 3 mm x 3 mm in cross-section, pentane as the working fluid, with the power inputs of up to 3 W. Due to the low Bond number (Bo) in microgravity and materials of construction, the CVB system was ideally suited to determine the contribution of the Marangoni forces toward the limiting heat pipe performance, and the transparent quartz shows exactly how that limitation occurs.Previous literature models and experimental temperature and pressure measurements suggested that at high enough temperature gradients, the working fluid should be subjected to enough Marangoni force to force it away from the heater and ultimately, dry out the hot end. The CVB experiment shows that high temperature gradients lead to a totally opposite behavior, i.e., 'flooding' of the heated end. Flooding of the heater end is attributed to a competition between Marangoni-induced flow due to high temperature gradients at the heater end and capillary return flow from the cooler. This creates a thick liquid layer in the corner of the cuvette at the heater end. At the point of flow balance, a thick layer of liquid is observed on the flat surface of the quartz cuvette. This is defined as the central drop. The region from the top of the heater end to the central drop is referred to as the interfacial flow region. The interfacial flow region develops at a power input of around 0.7W, and increases in length to the power input of 2 W. At 2 W, the strength of the Marangoni forces saturate. As a result, the forces in the flooded interfacial region are not able to push the liquid further into the capillary region and a further penetration of liquid down the axis of the heat pipe is arrested. As the power input is increased to nearly 3W, an increase in the vapor space is observed near the heater end at 3 W. This behavior suggests that the flooding might just be an intermediate stage in reaching the dry-out limitation.The flat quartz surface at the hot end is covered by a wavy thin liquid film due to the interfacial forces. The hot end region closest to the heater is a superheated vapor region that leads to the condensation. This additional observation is discussed in Appendix. (C) 2016 Elsevier Ltd. All rights reserved.